Lack of Appetite
This is generally a sign that your pug isn't feeling at all well. A pug might skip a meal once, but any more than that is something to worry about. Not wanting to eat can have any number of causes, from poor dental health (it hurts to chew) to viral diseases such as distemper or infectious canine hepatitis (not infectious to humans).
Any time your pug loses interest in food — especially if he's less active than usual, his tail is uncurled, or he shows other signs of not feeling well — take him to the veterinarian. This is a situation where your pug diary can come in handy. You'll be able to tell the veterinarian when your dog stopped eating and about any other unusual behaviors you may have noticed.